1. Technical Field
The present invention relates to a technique for calculating a toner consumption amount which is demanded for image formation in an image forming apparatus which forms an image using toner.
2. Related Art
Among image forming apparatuses which form images using toner is such an apparatus in which, in an attempt to obtain a good image quality, processes multi-level tone data and forms an image based on the processed image data. For instance, in the image forming apparatus which is described in Japanese Unexamined Patent Application Publication No. 2004-077873, the gamma characteristic of the apparatus is presumed from the detected densities of patch images which gradually span different tone levels, a characteristic which will cancel the gamma characteristic is given to image data, and an image of an excellent quality is formed without any influence exerted by a change of the gamma characteristic.
Meanwhile, for the purpose of grasping a remaining toner amount in the apparatus and properly managing consumables, an image forming apparatus of this type must be able to accurately calculate the amount of toner which is consumed to form an image. To this end, tone levels at print dots are integrated and a toner consumption amount is calculated based on this integrated value according to the technique described in Japanese Unexamined Patent Application Publication No. 2002-162800 for instance.
However, a tone level expressed by image data is not necessarily in proportion to an actual toner consumption amount. For example, an apparatus of this type generally performs data processing which will provide image data with a predetermined characteristic in order to improve an image quality. This maintains the image data and the density of an image eventually formed on a recording medium in a constant correlation. This data processing nevertheless does not always manage the correlation between the image data and the amount of toner constituting the image which has been formed. Further, it is known that the density of toner constituting an image and the density of the image hold a non-linear relationship with each other. These factors give rise to significant non-linearity between a tone level expressed by image data and a toner consumption amount, which could deteriorate the accuracy of calculating the toner consumption amount.